AEROLOGY OF EXTRATROPICAL DISTURBANCES 601 
daily synoptic work, could hardly be explained if fronts The very valuable daily synoptic weather maps pub- 
were phenomena restricted to the surface layer. Sys- lished by the United States Weather Bureau in co- 
tematic use of the frontal method of analysis of upper- operation with the Army, Navy, and Air Force confirm 
(1000 ft) km) 22mph 45 67 89mph 4QMPS 3OMPS. 2OMPS mb 
55 6 TO° 90 
16 
50-115 |~ ~+-4--_ 
14 
45 
13 
40-12 
tit 
35 
10 
30+ 9 
28 =20°. 
264 8 
24 
22 w —40° 
20+ 6 
18 
30° 
le 5 0. 
444 
12 -202 
10+-3 
8 
alr2 
441 
2 
o+o 
4OMPS 3OMPS. Zomps __ ™b. 
400°) = y= — 
==390- 100 
150 
200 
3208 
Ee - 
Sales IK 
24 400 
7 5 
20 
0 
0 A 500 
44 600 
fled 
(0-3 700 
er [ee 
6 800 
lie lime ee 
2 
@O-—=0) Es] 1000 
70°N 65° 60° 55° 50° 45° 40° 35° 30° 25° N 
Fic. 1.—Mean cross section for 0300 GMT, November 30, 1946, showing average distribution of geostrophic westerly wind and 
of temperature over North America from latitude 25° to 75°N in a case of approximately straight westerly flow. Heavy lines indi- 
cate boundaries of the principal frontal layer (polar front) and tropopauses. Thin solid lines indicate velocity of westerly wind 
component (meters per second and miles per hour), and dashed lines temperature (degrees centigrade) in top picture and potential 
temperature (degrees absolute) in lower picture. 
air charts, at least up to 500 mb, has shown that the existence of a band of strong isotherm concentration 
fronts are not only surface phenomena.'* at the 500-mb level. Over large parts of the Northern 
4, The method of drawing frontal contour charts, first used [Eeumsjolaes@ Un eae poowe alt ine One acbenisiice @ ic 
in the analysis of selected European cyclones [9, 10] and later real frontal zone; in other parts, however, Leis emnlOce 
extended to daily weather charts in Canada [18], is very useful diffuse. Since this band of crowded isotherms undergoes 
for a simple description of actual atmospheric conditions. strong meridional displacements from day to day, it 
